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1 U-Pb zircon dating of basement inliers within the 2 Moine Supergroup, Scottish Caledonides: implications of Archaean 3 protolith ages 4 5 C.R.L. Friend 1, R.A. Strachan2, P.D. Kinny 3 6 7 8 1. 45, Stanway Rd., Risinghurst, Headington, Oxford OX3 8HU, UK 9 10 2. School of Earth & Environmental Sciences, University of Portsmouth, Burnaby Road, 11 Portsmouth PO1 3QL, UK 12 13 3. The Institute for Geoscience Research, Department of Applied Geology, Curtin University of 14 Technology, GPO Box U1987, Perth, WA 6845, Australia 15 16 17 18 Abstract: Basement inliers within the Scottish Caledonides have been 19 conventionally correlated with the Archaean Lewisian Gneiss Complex of the Caledonian 20 foreland. Alternatively, the inliers could represent allochthonous accreted to 21 Laurentia before or during the Caledonian orogeny. SIMS U-Pb zircon dating indicates 22 that the Ribigill, Borgie, Farr and Western Glenelg basement inliers are characterized by 23 late Archaean protolith ages, and a period of isotopic disturbance in the late 24 Palaeoproterozoic. The data are broadly consistent with correlation between the inliers and 25 components of the Lewisian Gneiss Complex of the Caledonian foreland. The c. 2900 Ma 26 protolith ages support correlation of the Borgie and Farr inliers with the Assynt , 27 and a younger, c. 2800 Ma age for the Ribigill inlier supports correlation with the 28 Rhiconich terrane. None of the studied inliers shows a complete match of protolith and 29 early metamorphic histories with any of the Lewisian basement terranes, but differences 30 between the inliers and the foreland are no greater than those recorded within the foreland 31 basement terranes themselves. Therefore, it remains probable that the dated inlier 32 formed a distal part of the Laurentian margin prior to final telescoping during the 33 Caledonian orogeny. [end of abstract] 34 35 The complexity of many collisional orogens results, at least in part, from the tectonic 36 assembly of disparate crustal blocks to result in collages of -bounded ‘suspect’ or 37 ‘allochthonous’ terranes that have become detached from the cratons from whence they 38 originated. One of the main challenges in such a setting involves the identification of 11/12/06 Inliers -revised 2

39 individual terranes and their possible cratonic sources, and hence an evaluation of the 40 likely displacements along the terrane-bounding faults. In some Phanerozoic orogens the 41 history of terrane accretion and estimates of likely displacements along terrane boundaries 42 can be resolved by palaeomagnetic and palaeontological methods. In older orogens, 43 particularly those characterized by unfossiliferous strata and/or medium to high-grade 44 metamorphic rocks, identification of terranes and the nature of their original relationship to 45 cratonic foreland rocks is considerably more difficult. Correlation of a terrane with a 46 cratonic foreland requires the identification of common geological features, many of which 47 may have been eroded in older orogens. In such cases, a potential method of analysis 48 involves the characterization of basement rocks in a given terrane, and comparison with 49 the basement rocks of adjacent cratonic forelands. This method may encounter problems 50 as a result of the extensive reworking and resetting of isotopic systems that are common in 51 basement complexes and in orogens, but may be the only tool available for terrane 52 analysis. Despite the potential difficulties, this is the approach adopted in this paper where 53 U-Pb geochronology has been used to characterize basement inliers within the Lower 54 Palaeozoic Caledonide orogen of northwest Scotland, and to assess potential linkages with 55 the Laurentian foreland west of the Moine Thrust Zone (Fig 1). 56 Within the Caledonide orogen in northwest Scotland (Fig. 1), there are numerous 57 inliers of highly deformed gneissic rocks that differ markedly in their lithological 58 characteristics and structural and metamorphic histories from the adjacent 59 metasedimentary rocks of the Neoproterozoic Moine Supergroup (e.g. Flett 1905; Peach et 60 al. 1910). These inliers have the appearance of crystalline basement now variably 61 overprinted with younger structures, many of which have been interpreted as Caledonian 62 (Ordovician-Silurian) in age (e.g. Rathbone & Harris 1979; Strachan & Holdsworth 1988; 63 Holdsworth 1989). A central problem within the Scottish Caledonides concerns the extent 64 to which the basement inliers and the Moine Supergroup are allochthonous with respect to 65 the Laurentian foreland west of the Moine Thrust Zone (Fig. 1). The foreland comprises 66 the Archaean – Palaeoproterozoic Lewisian Gneiss Complex (e.g. Friend & Kinny 2001; 67 Park et al. 2002; Kinny et al. 2005) that is overlain unconformably by the late 68 Mesoproterozoic to Neoproterozoic Torridonian sedimentary rocks (e.g. Stewart 2002). 69 Mainly on lithological grounds, the basement inliers have been correlated previously with 70 the Lewisian Gneiss Complex (e.g. Johnstone 1975; Rathbone & Harris 1979), and the 71 Moine Supergroup sediments with the Torridonian (e.g. Cheeney & Matthews 1965). If 11/12/06 Inliers -revised 3

72 such correlations are correct, they imply that the basement inliers and the Moine rocks 73 evolved as part of Laurentia during the Precambrian. An alternative view is that these rock 74 units form part of an allochthonous terrane that was accreted to the Laurentian margin 75 either prior to or during the Caledonian orogeny (e.g. Bluck et al. 1997). 76 Attempts to evaluate Moine-Torridonian linkages have noted that the two 77 sequences have slightly different detrital zircon suites (Rainbird et al. 2001; Friend et al. 78 2003; see however, Krabbendam et al. 2008), and moreover the Moine rocks were affected 79 by mid-Neoproterozoic (Knoydartian) orogenic events that are apparently absent on the 80 foreland (e.g. Rogers et al. 1998; Vance et al. 1998; Tanner & Evans 2003). Nevertheless, 81 neither of these differences necessarily precludes a Laurentian origin for the Moine rocks 82 (Cawood et al. 2004). As an alternative method of evaluating potential linkages across the 83 Moine Thrust Zone we provide in this paper new isotopic age data for four basement 84 inliers within the Moine Supergroup. We assess the resultant implications for possible 85 linkages with the Lewisian Gneiss Complex of the Laurentian foreland and regional 86 tectonic models for this part of the Caledonides. 87 88 Regional setting of basement inliers within the Caledonides of NW Scotland 89 90 Lithologies and structural setting 91 92 Inliers of basement rocks occur widely within the Moine Supergroup, mainly in the Moine 93 and Sgurr Beag nappes, and largely in contact with metasediments assigned to the Morar 94 and Glenfinnan groups. There are three main concentrations of inliers: those in northern 95 below the Naver Thrust; those in the Scardroy-Fannich area; and those 96 immediately above the Moine Thrust in the Attadale – Glenelg – south Skye area (Fig. 1). 97 Numerous smaller inliers are also present within other parts of the Moine and Sgurr Beag 98 nappes. The inliers lie consistently at the lowest structural levels of local stratigraphical 99 successions once the effects of thrusting and/or folding are removed. Some inliers 100 apparently lie in the cores of isoclinal folds e.g. Morar (Kennedy 1955; Powell 1966) and 101 Naver (Strachan & Holdsworth 1988), whereas others are allochthonous slices underlain 102 by Caledonian thrusts such as the Sgurr Beag Thrust (e.g. Tanner et al. 1970; Rathbone & 103 Harris 1979) and the Ben Hope Thrust (Holdsworth 1989). 11/12/06 Inliers -revised 4

104 Most inliers are dominated by tonalitic to dioritic hornblende-rich gneisses that are 105 commonly highly deformed and variably banded with polyphase pegmatitic material. Thin 106 strips of pelitic metasediment and marble have been recognized in some inliers (e.g. Loch 107 Shin, Eastern Glenelg) and appear to represent an integral part of the basement 108 assemblage. Throughout all of the inliers, the dominant metamorphic assemblages now 109 present are amphibolite facies or lower, as the gneisses have been extensively reworked 110 and retrogressed during Knoydartian (820-730 Ma) and Caledonian (470-420 Ma) 111 orogenic events. Some inliers locally preserve evidence of high-grade, pre-Caledonian 112 metamorphic assemblages. These include the Western Glenelg inlier where relict granulite 113 facies mineralogies are preserved (e.g. Barber & May 1975; Sanders 1979) and the Eastern 114 Glenelg inlier where eclogite facies rocks are present (e.g. Teall 1891; Alderman 1936; 115 Mercy & O’Hara, 1969; Sanders 1979; Sanders et al. 1984). Early high-grade assemblages 116 have also been reported from the Borgie inlier where garnet and clinopyroxene-bearing 117 mafic gneisses were retrogressed into amphibole-plagioclase assemblages during the 118 Caledonian orogeny (Moorhouse 1976; Holdsworth et al. 2001). 119 120 Affinities of the basement inliers and relationships with the Moine Supergroup 121 122 When the basement inliers within the Moine Supergroup were first mapped they were 123 interpreted to be sub-Moine, Lewisian rocks because of their lithological similarity to the 124 Lewisian gneisses of the Caledonian foreland (e.g. Flett 1905; Peach et al. 1907, 1910, 125 1913). This correlation was challenged by Sutton & Watson (1953, 1954), who 126 interpreted the gneissic rocks of central Ross-shire as integral parts of the Moine 127 succession. However, subsequent research in the Glenelg area showed this to be incorrect 128 (Ramsay 1958) and correlation with the Lewisian of the foreland was reinstated and 129 continued in later studies of the Moine nappes (e.g. Sutton & Watson 1962; Barber & May 130 1975; Rathbone & Harris 1979; Strachan & Holdsworth 1988; Holdsworth 1989; 131 Temperley & Windley 1997). It has been tacitly assumed on the basis of broad lithological 132 similarities that all of the inliers belong to essentially the same portion of the Lewisian 133 (e.g. Sutton & Watson 1962; Watson 1975). However, the use of lithology alone as a basis 134 for correlation of complex gneissic rocks is no longer considered acceptable. This is 135 particularly the case when considering units that (prior to Caledonian thrusting) may have 136 formerly been separated by many tens or even hundreds of kilometres. Furthermore, it has 11/12/06 Inliers -revised 5

137 been shown that the itself comprises a variety of terranes of differing 138 age and history, some added in the Proterozoic (Kinny et al. 2005). 139 Following the early work that suggested that a tectonised unconformity existed 140 between the Moine and the basement (e.g. Peach et al. 1910, 1913), the present consensus 141 is that the Moine Supergroup was deposited unconformably on the basement inliers (Barr 142 et al. 1988; Holdsworth et al. 1994; Soper et al. 1998). In some places, way-up evidence 143 clearly shows that the Moine sedimentary rocks young away from the basement (e.g. 144 Bailey & Tilley 1952; Kennedy 1955; Ramsay 1958; Holdsworth 1989; Moorhouse et al. 145 1988), and basal Moine conglomerates are described from several localities, for example, 146 at Glenelg (e.g. Bailey & Tilley 1952; Ramsay 1958) and Attadale (Barber & May 1975). 147 Others, such as at Strathan (Mendum 1976) are more contentious. Some of the reported 148 ‘basal conglomerates’ (e.g. Glen Strathfarrar, Strathan) are now interpreted as being partly 149 of tectonic origin, probably arising from the disruption of quartz veins (Holdsworth et al. 150 2001; Friend & Strachan unpublished data) but this does not necessarily undermine the 151 essentially autochthonous status of the sub-Moine basement. As suggested by Tanner et 152 al. (1970), those inliers occurring along the trace of the Sgurr Beag Thrust in Ross-shire 153 may represent tectonically detached slices of a ‘basement high’, possibly representing 154 shoulders that separated the Morar and Glenfinnan-Loch Eil sedimentary basins (see also 155 Soper et al. 1998). 156 157 Previous isotopic data 158 159 To date, there have been few isotopic age determinations on the basement inliers, their 160 heterogeneity and complex metamorphic history creating difficulties for both whole rock 161 and mineral isotope studies. Moorbath & Taylor (1974) obtained a Rb-Sr whole-rock 162 isochron age of 2810 ± 120 Ma for the Scardroy inlier (Fig. 1) which they claimed to 163 “……prove beyond any doubt that the rocks of the Scardroy sheet are, indeed, Lewisian.” 164 Moorbath & Taylor (1974) also produced K-Ar dates on hornblendes and biotites from 165 Scardroy in the range 459-420 Ma (with one sample at 535 Ma interpreted to have 166 incompletely outgassed). These results were compared to unpublished data that Moorbath 167 and Taylor had obtained from the Eastern Glenelg inlier where similar Caledonian K-Ar 168 ages had been obtained, and contrasted with data from the Western Glenelg inlier where 169 K-Ar ages were in the range 2200-1600 Ma. Miller et al. (1963) produced a 1515 ± 104 11/12/06 Inliers -revised 6

170 Ma K-Ar age date on omphacite from the eclogitic rocks in the Eastern Glenelg inlier. A 171 subsequent study provided Sm-Nd mineral regression ages on the eclogites of 1082 ± 22 172 and 1010 ± 13 Ma that were interpreted to date a high-grade Grenvillian metamorphic 173 event (Sanders et al. 1984). The existence of this event has been broadly substantiated by 174 U-Pb titanite ages of c. 1000 Ma obtained from the Eastern Glenelg inlier (Brewer et al. 175 2003). 176 177 Analytical techniques 178 179 Zircons separated from the rock samples were mounted in epoxy resin, sectioned, imaged 180 by cathodoluminescence, and dated using the SHRIMP-II ion microprobe at the John de 181 Laeter Centre, Curtin University, Perth, Western Australia. Operating conditions for 182 SHRIMP were routine, namely 25 μm analytical spot size, primary beam current 2 to 5 183 nA, mass resolution 5000 (1% valley), and sensitivity for Pb isotopes approximately 15 184 cps/ppm/nA. Correction of isotope ratios for common Pb was based on the measured 185 204Pb, representing in most cases less than 1% correction to the 206Pb counts (see 186 %com.206Pb, Table 1), with the common Pb composition modelled upon that of Broken 187 Hill ore Pb. Pb/U isotopic ratios were corrected for instrumental inter-element 188 discrimination using the observed co-variation between 206Pb/238U and UO/U (Compston 189 et al. 1984, 1992) determined from interspersed analyses of the Perth standard zircon CZ3 190 (564 Ma; 206Pb/238U = 0.0914). The uncertainty in Pb/U ratios associated with this 191 correction procedure was in the range 1.5 to 2.5%, whereas uncertainties in Pb/Pb ratios 192 were generally lower, being governed principally by counting statistics. Isotope ratios and 193 corresponding ages (calculated using standard decay constants) are listed in Table 1, 194 together with 1σ uncertainties. Unless otherwise stated, all ages discussed in the text are 195 given with 95% confidence limits. 196 197 Results 198 199 S99/2: Ribigill inlier [National Grid Reference: NC 580547] 200 201 The Ribigill inlier (Fig. 1) occupies an antiformal fold core in the hanging wall of the Ben 202 Hope Thrust (Moorhouse & Moorhouse 1977; Holdsworth 1989; British Geological 11/12/06 Inliers -revised 7

203 Survey 1997; Holdsworth et al. 2001). Of the three inliers examined along the north coast, 204 the Ribigill inlier is the structurally lowest and the least far travelled with respect to the 205 Caledonian foreland. The sample analysed was collected from a quarry in the central 206 portion of the inlier that is dominated by banded, quartzo-feldspathic gneisses that are 207 broadly granodioritic in composition. The gneissic layering consists of mm−cm scale 208 alternations of mafic- and felsic-dominated layers. Some of the latter comprise deformed 209 concordant layers and lenticles of granitic suggesting either that the rocks were 210 invaded by melt, or that they underwent a metamorphic event that induced a low degree of 211 partial melting. This melt material was avoided in the sampling. In thin-section, the 212 sample comprises a medium- to coarse-grained, granoblastic assemblage of plagioclase 213 and K-feldspar, hornblende, biotite, epidote and quartz. 214 The separated zircons were euhedral to subhedral prismatic grains. CL imaging 215 revealed regular internal growth zoning in most grains and occasional structural cores 216 (Figure 2). The analysed zircons produced a range of 207Pb/206Pb ages, and plot either 217 overlapping concordia or slightly below (Fig. 2). Of the three analyses with highest 218 207Pb/206Pb, two (1.1, 4.1, Table 1) were situated in discrete structural cores, suggesting 219 that they may represent inherited components in the protolith. The combined age of these 220 three analyses is 2822 ± 28 Ma. The main group of analyses record 207Pb/206Pb ages of 221 between 2760 and 2660 Ma. These probably represent the main protolith population. In 222 addition, three analyses of tips of grains with high U content and low Th/U ratio (3.2, 2.3, 223 5.1, Table 1) and appearing dark in CL (Fig. 2), record younger apparent ages, appearing 224 to lie on a discordance line trending towards a c. 1600 Ma intercept age, adjacent to 225 analysis 5.1. The formation of these rims could be related to the episode responsible for 226 the -pegmatite layers observed in the host rock. 227 228 S96/12: Borgie inlier [NC 689573] 229 230 The Borgie inlier is the largest on the north coast (Fig. 1) and occupies a structurally 231 higher antiformal fold core between the Ben Hope Thrust and the Naver Thrust 232 (Moorhouse 1976; British Geological Survey 1997; Holdsworth et al. 2001). It contains a 233 range of different lithologies. The banded felsic gneisses of the inlier are K-feldspar poor, 234 and variably hornblende- and biotite-bearing; locally they enclose rafts of mafic and 235 ultramafic rocks. Some of the mafic rafts are characterized by garnet-clinopyroxene 11/12/06 Inliers -revised 8

236 metamorphic assemblages (Moorhouse 1976; Holdsworth et al. 2001). In thin section, the 237 analysed sample is banded and comprises a coarse, granoblastic assemblage of plagioclase 238 feldspar and quartz with finer-grained, porphyroblastic hornblende and oriented flakes of 239 biotite with minor chlorite. Some mafic-dominated layers comprise aligned biotite and 240 granular epidote. The quartz-rich domains are dominated by annealed ribbon textures, 241 suggesting that the gneiss has undergone high strain. 242 The separated zircons typically have sub-rounded, modified shapes, and CL 243 imaging revealed that numerous grains have a brightly luminescent mantle over a zoned 244 interior. On a concordia diagram, the analysed points form a coherent discordance array 245 that projects on a shallow trajectory from a late Archaean upper intercept age towards an 246 approximately end-of-Palaeoproterozoic lower intercept age (Fig. 3). The data are 247 interpreted to represent a single disturbed population. The least discordant analyses have 248 207Pb/206Pb ages of c. 2880 Ma, but there are too few of them to allow a more accurate 249 assessment of the protolith age. The projected lower intercept is c. 1600 Ma, suggesting 250 significant isotopic disturbance at about that time. 251 252 S99/1: Farr inlier [NC 687614] 253 254 The Farr inlier (Fig. 1) occupies the core of an isoclinal fold within the migmatitic Moine 255 rocks of the Naver Nappe (Moorhouse 1979; Moorhouse et al. 1988). It represents the 256 structurally highest inlier examined and is likely to be the furthest travelled relative to the 257 Caledonian foreland. The inlier is dominated by banded, mafic and intermediate 258 hornblendic gneisses that are highly deformed. The sample dated is coarse-grained gneiss 259 and in thin section comprises sub-equigranular, granoblastic plagioclase feldspar, quartz 260 and hornblende. Minor biotite may be retrogressive and accessory phases include 261 opaques, apatite and zircon. 262 The separated zircons were typically elongate, subhedral, prismatic grains, with a 263 narrow CL-bright rim evident on most grains, developed over regularly zoned interiors 264 (Fig. 4). Two SHRIMP analyses were undertaken on most grains, one spot in the core and 265 one on the rim. On a concordia diagram, the combined analyses form a broad, essentially 266 continuous discordant array projecting from a late Archaean upper intercept age to an end- 267 of-Palaeoproterozoic lower intercept age (Fig. 4). There is no clear distinction between 268 the age spectra for cores and rims other than that the analyses of rims tend to be the most 11/12/06 Inliers -revised 9

269 highly discordant. The four least-discordant analyses of grain cores have a combined age 270 of 2905 ± 24 Ma, which can be considered as a reasonable estimate of the protolith age of 271 this gneiss. The shallow slope of the discordance array suggests isotopic disturbance of 272 the zircons involving Pb-loss as early as c. 1600 Ma. 273 274 S96/41: Western Glenelg inlier, at Dornie [NG 912226] 275 276 This sample was taken from one of the high strain zones within the retrogressed gneisses 277 exposed in road cuttings near Dornie along the shore of Loch Duich (Fig. 1). The sample 278 is blastomylonitic and fine-grained with granoblastic quartz grains pseudomorphing ribbon 279 fabrics. The sample was taken in the hope that some indication of the 280 associated with the shearing event might be present. 281 The zircons from this sample showed typical igneous zonation features under CL 282 imaging, a minority of grains possessing a structural core (Fig. 5). Analyses produced a 283 range of late Archaean to Mesoproterozoic apparent ages. The oldest age obtained (c. 284 2800 Ma) was recorded from a spot within a structural core (analysis 5.1, Table 1). The 285 main population of least disturbed zircon is represented by five analyses (10.1, 11.1, 12.1, 286 15.1, 17.1, Table 1), which record a mean 207Pb/206Pb age of 2677 ± 16 Ma (Fig. 5). 287 Numerous discordant points trend to lower 207Pb/206Pb ages, following discordant arrays 288 that trending towards different lower intercept ages. The analyses recording the youngest 289 apparent ages include rim analyses (e.g. 14.2, 16.2) and three analyses of grain 9 (Table 1). 290 These analyses appear to lie on a secondary discordance line projecting from a late 291 Palaeoproterozoic upper intercept to younger apparent ages, implying a complex 292 multistage history of isotopic disturbance. 293 294 Comparison with the Lewisian Gneiss Complex of the foreland 295 296 The new data show that each of the inliers dated has an Archaean protolith. The wide 297 geographic distribution of the inliers dated suggests that the intervening inliers are of 298 similar age, although this remains to be proven. Amongst the northern inliers, the Ribigill 299 (c. 2760 Ma with c. 2820 Ma inherited components) appears to be younger than the Borgie 300 and Farr inliers (c. 2900 Ma), whilst the western Glenelg sample appears still younger at c. 301 2680 Ma (with one c. 2800 Ma core). All three of the northern inliers show similar 11/12/06 Inliers -revised 10

302 discordant patterns, reflecting disturbance of protolith grains in latest Palaeoproterozoic 303 times. The zircons from Glenelg show a broadly similar pattern, but with evidence for 304 additional disturbance during younger events. Distinct rims on the Farr and Ribigill inlier 305 zircons appear to have formed in the late Archaean and to have been disturbed in the 306 Proterozoic along with the enclosed cores, whereas some young components in the 307 Glenelg sample may represent components newly grown during Proterozoic events. 308 Are there any points of similarity between these inliers and the various components 309 of the Lewisian Gneiss Complex of the Caledonian foreland? The age range of the least 310 disturbed protolith zircons within the Ribigill inlier falls within that of the known 311 protoliths of the geographically adjacent Rhiconich terrane on the foreland (2840–2680 312 Ma). However, the Ribigill gneisses do not appear to contain any examples of the 313 extensive c. 1855 Ma granite sheets that are found throughout the Rhiconich terrane (e.g. 314 Kinny & Friend 1997; Kinny et al. 2005) and the analysed zircons do not appear to show 315 any new growth at this time. On the other hand, the timing of amphibolite facies 316 metamorphism in the Rhiconich terrane, c. 1740 Ma, is broadly consistent with the age of 317 some ancient Pb loss from the Ribigill zircons. The Ribigill inlier therefore displays some 318 similarities with the foreland basement. 319 The c. 2900 Ma protolith ages obtained from the Farr and Borgie inliers are older 320 than the typical protolith ages of the Rhiconich terrane. However, given that they represent 321 minimum age estimates from disturbed populations, they are a closer match to protolith 322 ages of the Assynt terrane (3030–2960 Ma). Significantly, there is no conclusive evidence 323 in the analysed zircons from any of the inliers for any major disturbance or new zircon 324 growth during either of the high-grade metamorphic events now recognized in the 325 Lewisian Gneiss Complex on the foreland: c. 2730 Ma in the Gruinard terrane (Love et al. 326 2003) and c. 2490 Ma in the Assynt terrane (Friend & Kinny 1995). Both events caused 327 U-depletion, and in the case of the c. 2490 Ma event, it was particularly intense and is very 328 easily recognised analytically in the zircons. Although the metamorphic assemblages of 329 the inliers are largely now amphibolite facies, it might be expected that the zircons would 330 have preserved evidence of this severe U-depletion, as found in extensive overgrowth 331 development in both the granulite and retrogressed granulite facies gneisses of the foreland 332 (e.g. Friend & Kinny 1995; Love et al. 2003). That such effects are absent is strong 333 evidence to suggest that the rocks did not experience either of these events. The Borgie 334 and Farr inliers could, therefore, have been derived from crustal material similar to the 11/12/06 Inliers -revised 11

335 Assynt terrane with protolith ages of c. 2900 Ma but which never attained granulite facies 336 conditions at 2490 Ma. Alternatively, they may have been derived from a different crustal 337 block that underwent a different tectono-metamorphic history. 338 The protolith age of the Western Glenelg inlier (c. 2680 Ma) is younger than the 339 majority of protolith ages obtained from the mainland Lewisian Gneiss Complex as well as 340 from the Outer (e.g. Kinny et al. 2005). However, given the high degree of 341 isotopic disturbance to the zircons, the potential affinities of this inlier with the Lewisian 342 foreland terranes cannot be determined with confidence. 343 In summary, although the zircon age spectra might support correlation of the 344 Borgie and Farr inliers with the Assynt terrane and the Ribigill inlier with the Rhiconich 345 terrane, there is no complete match of both protolith and metamorphic histories of any of 346 the inliers with any of the foreland basement terranes. However, these differences are no 347 greater than those between the individual terranes that form the Lewisian Gneiss Complex 348 itself. The lack of specific correlation is not unexpected given the likely c. 100 km 349 displacements along the Caledonian Moine Thrust Zone (e.g. Elliott & Johnson 1980; 350 Soper & Barber 1982; Butler & Coward 1984). It is noteworthy that the main period of 351 isotopic disturbance to the zircon populations in all four inlier samples was in the late 352 Palaeoproterozoic, broadly corresponding to the timing of episodes of amphibolite facies 353 reworking in the Lewisian foreland terranes (1740 – 1670 Ma) (e.g. Friend & Kinny 2001; 354 Kinny et al. 2005). 355 356 Conclusions 357 358 U-Pb zircon geochronology has shown that the Ribigill, Borgie, Farr and Western Glenelg 359 basement inliers are all characterized by late Archaean protolith ages and a period of 360 isotopic disturbance in the late Palaeoproterozoic. In broad terms, the data are consistent 361 with correlation between the inliers and components of the Lewisian Gneiss Complex of 362 the Caledonian foreland. In particular, the older, c. 2900 Ma protolith ages support 363 correlation of the Borgie and Farr inliers with the Assynt terrane, whilst the younger, c. 364 2800 Ma age for the Ribigill inlier supports correlation with the Rhiconich terrane. None 365 of the studied inliers shows a complete match of both its protolith and early metamorphic 366 histories with any of the Lewisian basement terranes, but differences between the inliers 367 and the foreland are no greater than those recorded within the foreland basement terranes 11/12/06 Inliers -revised 12

368 themselves. It is therefore probable that the dated inlier gneisses formed a distal part of 369 the Laurentian margin prior to final telescoping during the Caledonian orogeny. The 370 results of this study demonstrate the difficulty in assessing potential basement terrane 371 linkages across an orogenic front such as the Moine Thrust when reworking has 372 substantially disturbed isotopic systematics such that pre-thrusting protolith and 373 metamorphic histories cannot be matched with confidence. 374 375 Acknowledgements, 376 We thank Ian Burns for assistance in sample collection, and participants in the 2003 377 Highland Field Workshop for discussions in the field. John Mendum, Martin Whitehouse 378 and Maarten Krabbendam are thanked for constructive reviews that improved the paper. 379 380 381 References 382 Alderman, A.R. 1936. Eclogites from the neighbourhood of Glenelg, Inverness-shire. Quarterly 383 Journal of the Geological Society of London, 120, 153-192. 384 Bailey, E.B. & Tilley, C.E. 1952. Rocks claimed as conglomerate at the Moinian-Lewisian 385 junction. Report XVIII International Geological Congress G.B, 1948, part XIII, 272. 386 Barber, A.J. & May, F. 1975. The history of the Western Lewisian in the Glenelg inlier, Lochalsh, 387 Northern Highlands. Scottish Journal of Geology, 12, 35-50. 388 Barr, D., Strachan, R.A., Holdsworth, R.E. & Roberts, A.M. 1988. Summary of the Geology. In: 389 Allison, I., May, F. & Strachan, R.A. (eds) An Excursion Guide to the Moine Geology of the 390 . Scottish Academic Press, Edinburgh, 11-38. 391 Bluck, B.J., Dempster, T.J. & Rogers 1997. Allochthonous metamorphic blocks on the Hebridean 392 passive margin, Scotland. Journal of the Geological Society, London, 154, 921-924. 393 Brewer, T.S., Storey, C.D., Parrish, R.R., Temperley, S. & Windley, B.F. 2003. Grenvillian age 394 decompression of eclogites in the Glenelg-Attadale inlier, NW Scotland. Journal of the 395 Geological Society, London, 160, 565-574. 396 British Geological Survey. 1997. Tongue. Scotland Sheet 114E. Solid Geology. 1:50,000. British 397 Geological Survey, Keyworth, Nottingham. 398 Butler, R.W.H. & Coward, M.P. 1984. Geological constraints, structural evolution and the deep 399 geology of the NW Scottish Caledonides. , 3, 347-365. 400 Cheeney, R.F. & Matthews, D.W. 1965. The structural evolution of the Taskavaig and Moine 401 nappes in Skye. Scottish Journal of Geology, 1, 256-281. 11/12/06 Inliers -revised 13

402 Compston, W., Williams, I.S. & Meyer, C. 1984. U-Pb geochronology of zircons from Lunar 403 breccia 73217 using a sensitive high mass-resolution ion microprobe. Proceedings of the 404 Fourteenth Lunar and Planetary Conference, Pt. 2. Journal of Geophysical Research, 89, 405 Supplement, B525-534. 406 Compston, W., Williams, I.S., Kirschvink, J.L., Zhang Zichao & Ma Guogan. 1992. Zircon U-Pb 407 ages for the early Cambrian timescale. Journal of the Geological Society, London, 149, 171- 408 184. 409 Dewey, J.F. & Strachan R.A. 2003. Changing Silurian – Devonian relative plate motion in the 410 Caledonides: sinistral transperssion to sinistral transtension. Journal of the Geological Society 411 of London, 160, 219-229. 412 Elliott, D. & Johnson, M.R.W. 1980. Structural evolution in the northern part of the Moine Thrust 413 belt, NW Scotland. Transactions Royal Society of Edinburgh, 71, 69-96. 414 Flett, J.S. 1905. On the Petrographic Characters of the Inliers of Lewisian Rocks among the 415 Moine Gneisses of the North of Scotland. Memoirs of the Geological Survey. Summary of 416 progress for 1905, 155-167. 417 Friend, C. R. L. & Kinny, P.D. 1995. New evidence for the protolith ages of Lewisian granulites, 418 northwest Scotland. Geology, 23, 1027-1030. 419 Friend, C.R.L. & Kinny, P.D. 2001. A reappraisal of the Lewisian Gneiss Complex: 420 geochronological evidence for tectonic assembly of disparate terranes in the Proterozoic. 421 Contributions to Mineralogy and Petrology, 142, 198-218. 422 Friend, C.R.L., Strachan, R.A., Kinny, P.D. & Watt, G.R. 2003. Provenance of the Moine 423 Supergroup of NW Scotland: evidence from geochronology of detrital and inherited zircons 424 from sediments, and migmatites. Journal of the Geological Society, London, 160, 247- 425 258. 426 Holdsworth, R.E. 1989. The geology and structural evolution of a Caledonian fold and ductile 427 thrust zone, Kyle of Tongue region, Sutherland, northern Scotland. Journal of the Geological 428 Society, London, 146, 809-823. 429 Holdsworth, R.E., Strachan, R.A. & Harris, A.L. 1994. Precambrian rocks in northern Scotland 430 east of the Moine Thrust: the Moine Supergroup. In: Gibbons, W. & Harris, A.L. (eds) A 431 revised correlation of Precambrian rocks in the British Isles. Geological Society, London, 432 Special Reports, 22, 23-32. 433 Holdsworth, R.E., Strachan, R.A. & Alsop, G.I. 2001. Geology of the Tongue District. Memoir of 434 the British Geological Survey, HMSO. 435 Johnstone, G.S. 1975. The Moine Succession. In: Harris, A.L., Shackleton, R.M., Watson, J.V., 436 Downie, C., Harland, W.B. & Moorbath, S. (eds) A Correlation of Precambrian Rocks in the 437 British Isles. Geological Society, London, Special Report, 6, 30-42. 11/12/06 Inliers -revised 14

438 Kennedy, W.Q. 1955. The tectonics of the Morar anticline and the problem of the North-West 439 Caledonian Front. Quarterly Journal of the Geological Society, London, 110, 357-382. 440 Kinny, P.D. & Friend, C.R.L.1997. U-Pb isotopic evidence for the accretion of different crustal 441 blocks to form the Lewisian Complex of Northwest Scotland. Contributions to Mineralogy 442 and Petrology, 129, 326-340. 443 Kinny, P.D., Friend, C.R.L. & Love, G.J. 2005. Proposal for a terrane-based nomenclature for the 444 Lewisian Gneiss Complex of NW Scotland. Journal of the Geological Society, London, 162, 445 175-186. 446 Krabbendam, M., Prave, A.R. & Cheer, D. 2008. A fluvial origin for the Neoproterozoic Morar 447 Group, NW Scotland: implications for Torridon-Morar group correlation and the Grenville 448 Orogen foreland basin. Journal of the Geological Society, London, in press. 449 Love, G.J., Kinny, P.D. & Friend, C.R.L. 2003. Timing of magmatism and metamorphism in the 450 Gruinard Bay area of the Lewisian Gneiss Complex: comparisons with the Assynt Terrane and 451 implications for terrane accretion. Contributions to Mineralogy and Petrology, 146, 620-636. 452 Mendum, J. 1976. A strain study of the Strathan conglomerate, north Sutherland. Scottish Journal 453 of Geology, 12, 159-165. 454 Mercy E.L.P. & O’Hara, M.J. 1969. Nepheline normative eclogite from Loch Duich, Ross-shire. 455 Scottish Journal of Geology, 4, 1-9. 456 Miller, J.A., Barber, A.J. & Kempton, N.H. 1963. A potassium/argon age determination from a 457 Lewisian inlier. Nature, 197, 1095-1096. 458 Moorbath, S. & Taylor, P.N. 1974. A Lewisian age for the Scardroy mass. Nature 250, 41-43. 459 Moorhouse, S.J. 1976. The geochemistry of the Lewisian and Moinian of the Borgie area, North 460 Sutherland. Scottish Journal of Geology, 12, 159-165. 461 Moorhouse, S.J. & Moorhouse, V.E. 1977. A Lewisian basement sheet at Ribigill, north 462 Sutherland. Scottish Journal of Geology, 13, 289-300. 463 Moorhouse, S.J., Moorhouse, V.E., & Holdsworth, R.E. 1988. Excursion 12. North Sutherland. 464 In: Allison, I., May, F. & Strachan, R.A. (eds) An Excursion Guide to the Moine Geology of 465 the Scottish Highlands. Scottish Academic Press, Edinburgh, 216-248. 466 Moorhouse, V.E. 1979. The geology and geochemistry of the Bettyhill-Strathy area of north-east 467 Sutherland. PhD thesis, University of Hull. 468 Park, R.G., Stewart, A.D. & Wright, D.T. 2002. The Hebridean Terrane. In: Trewin, N. (ed) The 469 . Geological Society, London, 45-80. 470 Peach, B.N., Horne, J., Gunn, W., Clough, C.T., Hinxman, L.W. & Teall, J.J.H. 1907. The 471 Geological Structure of the North West Highlands of Scotland. Memoir of the Geological 472 Survey, United Kingdom. 11/12/06 Inliers -revised 15

473 Peach, B.N., Horne, J., Woodward, H.B., Clough, C.T., Harker, A. & Wedd, C.B. 1910. The 474 geology of Glenelg, Lochalsh and South-east part of Skye. Memoir of the Geological Survey, 475 United Kingdom. 476 Peach, B.N., Horne, J., Hinxman, L.W., Crampton, C.B. Anderson, E.M. & Carruthers, R.G. 1913. 477 The geology of central Ross-shire. Memoir Geological Survey United Kingdom. 478 Powell, D. 1966. The structure of the south-eastern part of the Morar antiform, Inverness-shire. 479 Proceedings of the Geologists Association, 77, 79–100. 480 Rainbird, R.H., Hamilton, M.A. & Young, G.M. 2001. Detrital zircon geochronology and 481 provenance of the Torridonian, NW Scotland. Journal of the Geological Society, London, 158, 482 15-27. 483 Ramsay, J. G. 1958. Moine-Lewisian relations at Glenelg, Invernessshire. Quarterly Journal of the 484 Geological Society, London, 113, 99-106. 485 Rathbone, P.A. & Harris, A.L. 1979. Basement-cover relationships at Lewisian inliers in the Moine 486 rocks. In: Harris, A.L., Holland, C.H. & Leake, B.E. (eds), The Caledonides of the British 487 Isles - reviewed. Geological Society of London, Special Publication 8, 101-107. 488 Rogers, G., Hyslop, E.K., Strachan, R.A., Paterson, B.A. & Holdsworth, R.E. 1998. The structural 489 setting and U-Pb geochronology of Knoydartian in Inverness-shire: evidence for 490 Neoproterozoic tectonothermal events in the Moine of NW Scotland. Journal of the Geological 491 Society, London, 155, 685-696. 492 Sanders, I.S. 1979. Observations on eclogite- and granulite-facies rocks in the basement of the 493 Caledonides. In: Harris, A.L., Holland, C.H. & Leake, B.E. (eds), The Caledonides of the 494 British Isles reviewed. Geological Society of London, Special Publication 8, 97-101. 495 Sanders, I.S., van Calsteren, P.W.C. & Hawksworth, C.J. 1984. A Grenville Sm-Nd age for the 496 Glenelg eclogite in north-west Scotland. Nature 312, 439-440. 497 Soper, N.J. & Barber, A.J. 1982. A model for the deep structure of the Moine thrust zone . 498 Journal of the Geological Society, London, 139, 127-138. 499 Soper, N.J., Harris, A.L. & Strachan, R.A. 1998. of the Moine Supergroup: a 500 synthesis. Journal of the Geological Society, London. 155, 13-24. 501 Stewart, A.D. 2002. The later Proterozoic Torridonian rocks of Scotland: their sedimentology, 502 geochemistry and origin. Geological Society, London, Memoir, 24. 503 Strachan, R.A. & Holdsworth, R.E. 1988. Basement-cover relationships and structure within the 504 Moine rocks of central and southeast Sutherland. Journal of the Geological Society, London, 505 145, 23-36. 506 Sutton, J. & Watson, J. 1953. The supposed Lewisian inlier of Scardroy, central Ross-shire, and 507 its relations with the surrounding Moine rocks. Quarterly Journal of the Geological Society, 508 London, 108, 99-106. 11/12/06 Inliers -revised 16

509 Sutton, J. & Watson, J. 1954. The structure and stratigraphical succession of the Moines of 510 Fannich Forest and Strath Bran, Ross-shire. Quarterly Journal of the Geological Society, 511 London, 110, 21-54. 512 Sutton, J. & Watson, J. 1962. An interpretation of Moine-Lewisian relations in central Ross-shire. 513 Geological Magazine 99, 527-541. 514 Tanner, P.W.G. & Evans, J.A. 2003. Late Precambrian U-Pb titanite age for peak regional 515 metamorphism and deformation (Knoydartian orogeny) in the western Moine, Scotland. 516 Journal of the Geological Society 160, 555-564. 517 Tanner, P.W.G., Johnstone, G.S., Smith, D.I. & Harris, A.L. 1970. Moinian Stratigraphy and the 518 problem of the Central Ross-shire Inliers. Bulletin of the Geological Society of America, 81, 519 299-306. 520 Teall, J.J.H. 1891. On eclogite from Loch Duich. Mineralogical Magazine, 9, 217-218. 521 Temperley, S. & Windley, B.F. 1997. Grenvillian in northwest Scotland. 522 Geology, 25, 53-56. 523 Vance, D., Strachan, R.A. & Jones, K.A. 1998. Extensional versus compressional settings for 524 metamorphism: garnet chronometry and pressure-temperature-time histories in the Moine 525 Supergroup, northwest Scotland. Geology, 26, 927-930. 526 Watson, J.V. 1975. The Lewisian Complex. In: Harris, A.L., Shackleton, R.M., Watson, J.V., 527 Downie, C., Harland, W.B. & Moorbath, S. (eds) A Correlation of Precambrian Rocks in the 528 British Isles. Geological Society, London, Special Report, 6, 15-29. 529 530 Tables 531 532 Table 1. SIMS U-Th-Pb data for the analysed zircons from basement inliers. Key to spot positions: 533 unless otherwise stated, analytical spots were centrally located. ‘Core’ implies a visible structural 534 core and ‘rim’ implies a distinct overgrowth. Otherwise, the terms ‘centre’ and ‘outer’ and/or ‘tip’ 535 are used. ‘Patchy’ indicates a domain lacking in concentric growth zonation. Detailed spot 536 locations are unfortunately not available for the Borgie sample. 537 538 Figure captions 539 540 Figure 1. Sketch map of northern Scotland showing the position of the Moine Supergroup 541 with the main basement inliers, and the locations of the analysed samples. Abbreviations: 542 MT, Moine Thrust; NT, Naver Thrust; SBT, Sgurr Beag Thrust; SkT, Skinsdale Thrust; St, 543 Strathan; LS, Loch Shin; F, Fannich; SC, Scardroy; S, Glen Strathfarrar; G, Glenelg; A, 544 Attadale. Inset box shows position of the study area. 11/12/06 Inliers -revised 17

545 546 Figure 2. Concordia plot for sample S99/2 Ribigill inlier, including cathodoluminescence 547 images of representative grains. Identified grain numbers are listed in Table 1, with the 548 approximate locations of SHRIMP analytical spots indicated by white circles. 549 550 Figure 3. Concordia plot for sample S96/12 Borgie inlier. 551 552 Figure 4. Concordia plot for sample S99/1 Farr inlier, including cathodoluminescence 553 images of representative grains. Identified grain numbers are listed in Table 1, with the 554 approximate locations of SHRIMP analytical spots indicated by white circles. 555 556 Figure 5. Concordia plot for sample S96/41 Western Glenelg inlier, including 557 cathodoluminescence images of representative grains. Identified grain numbers are listed 558 in Table 1, with the approximate locations of SHRIMP analytical spots indicated by white 559 circles. 560 561

0.6 Ribigill Inlier, Moine Nappe 3000

structural cores

U 1.1

4.1 0.5 rims 2600

Pb/ 3.2 6.1 206 238 2.3

0.4 6 8

1800 5 0.3 7 5.1

207Pb/ 235U 0.2 048121620 0.6 Borgie Inlier, Moine Nappe 3000

2800 U

0.5 2600 Pb/

206 238 2400

2200 0.4 2000

0.3

207Pb/ 235 U 0.2 4 6 8 10 12 14 16 18 0.7

Farr Inlier, Naver Nappe 3000 0.6 U structural cores 12.2 13.2 0.5 Pb/ 4.2

206 238 2500 1.1

20.1 0.4 2000 10 17.2 16.2 0.3 18.2 1500 9 8 7 0.2 11.2 6 207Pb/ 235U 0.1 048121620 3000 0.6 Glenelg Inlier (west)

U structural cores 5.1 0.5 2500 rims 17.1 Pb/ 1.1 206 238 0.4 2000 14 12 0.3 6.1 1500 16.2 14.2 11 gr 9 0.2 15 10 207Pb/ 235U 0.1 0 4 8 12 16 20

Grain. Position U Th Th/U %com 207Pb/206Pb ± 1σ 206Pb/238U ± 1σ 207Pb/235U ± 1σ 206Pb/238U 207Pb/206Pb Spot ppm ppm 206Pb Age ± 1σ Age ± 1σ

Ribigill inlier s99/2

1.1 core 142 108 0.76 0.17 0.2005 0.0012 0.5469 0.0135 15.12 0.39 2812 56 2830 10 8.1 centre 91 51 0.55 0.34 0.1989 0.0015 0.5041 0.0126 13.82 0.37 2632 54 2817 12 4.1 core 79 30 0.39 0.14 0.1985 0.0017 0.5220 0.0132 14.28 0.39 2708 56 2814 14 6.1 core 57 20 0.36 0.56 0.1928 0.0023 0.4812 0.0124 12.79 0.38 2533 54 2766 19 3.1 centre 182 81 0.44 0.17 0.1917 0.0012 0.5403 0.0133 14.28 0.37 2785 56 2757 10 2.1 centre 541 44 0.08 0.06 0.1875 0.0005 0.5118 0.0123 13.23 0.32 2664 53 2721 4 1.2 outer 125 97 0.78 0.18 0.1867 0.0011 0.5340 0.0132 13.75 0.36 2758 55 2714 10 6.2 outer 86 86 1.00 0.48 0.1865 0.0016 0.4973 0.0126 12.79 0.36 2602 54 2711 14 7.1 centre 197 79 0.40 0.40 0.1842 0.0018 0.4420 0.0110 11.22 0.31 2360 49 2691 16 4.2 outer 130 95 0.73 0.25 0.1833 0.0013 0.5131 0.0127 12.97 0.34 2670 54 2683 11 2.2 outer 90 84 0.94 0.24 0.1808 0.0015 0.5179 0.0130 12.91 0.35 2690 55 2660 14 5.2 outer 90 69 0.77 0.35 0.1796 0.0018 0.4489 0.0113 11.12 0.31 2390 50 2649 16 3.2 tip 332 9 0.03 0.06 0.1699 0.0007 0.4677 0.0114 10.96 0.28 2474 50 2556 6 2.3 tip 375 49 0.13 0.06 0.1518 0.0006 0.4388 0.0106 9.19 0.23 2345 48 2366 7 5.1 dark rim 1145 96 0.08 0.07 0.1057 0.0003 0.2836 0.0068 4.13 0.10 1609 34 1726 6

Borgie inlier s96/12

94.1 44 20 0.47 0.13 0.2078 0.0015 0.5620 0.0063 16.10 0.22 2875 26 2888 12 75.1 133 70 0.52 0 0.2063 0.0007 0.5463 0.0048 15.54 0.15 2810 20 2877 6 9.1 90 28 0.31 0 0.2026 0.0016 0.5367 0.0074 14.99 0.25 2770 31 2847 13 10.1 21 6 0.30 0.15 0.2010 0.0049 0.4625 0.0111 12.82 0.46 2451 49 2834 39 28.1 732 62 0.09 0 0.1965 0.0005 0.5297 0.0051 14.35 0.15 2740 22 2797 4 87.1 617 73 0.12 0.03 0.1937 0.0004 0.4652 0.0035 12.42 0.10 2462 15 2774 3 13.1 82 16 0.20 0.11 0.1936 0.0020 0.4876 0.0071 13.01 0.24 2560 31 2773 17 68.1 51 11 0.22 0.15 0.1920 0.0015 0.4559 0.0049 12.07 0.17 2422 22 2759 13 6.2 18 16 0.89 0.26 0.1916 0.0030 0.4436 0.0070 11.72 0.27 2367 31 2756 26 10.2 21 19 0.91 0.31 0.1916 0.0032 0.4822 0.0071 12.74 0.30 2537 31 2756 27 85.1 197 34 0.17 0.05 0.1857 0.0007 0.3814 0.0032 9.77 0.09 2083 15 2705 6 38.1 29 8 0.28 0.10 0.1801 0.0044 0.4089 0.0090 10.15 0.35 2210 41 2653 40 9.2 33 18 0.54 0.49 0.1775 0.0024 0.3469 0.0043 8.49 0.17 1920 21 2630 23 17.1 30 10 0.32 0.28 0.1766 0.0037 0.4493 0.0095 10.94 0.34 2392 42 2621 35 17.2 43 40 0.92 0.31 0.1736 0.0018 0.4044 0.0047 9.68 0.16 2189 22 2593 17 88.1 31 28 0.91 0.38 0.1674 0.0023 0.3747 0.0048 8.65 0.17 2052 22 2532 23 11.1 37 8 0.22 0.17 0.1670 0.0039 0.3136 0.0063 7.22 0.24 1758 31 2528 39 6.1 27 8 0.29 0.60 0.1647 0.0047 0.3814 0.0086 8.66 0.33 2083 40 2504 48

Farr inlier s99/1

13.2 core 72 34 0.48 0.06 0.2126 0.0018 0.5388 0.0138 15.79 0.44 2778 58 2925 14 4.2 core 56 59 1.05 0.18 0.2100 0.0020 0.5233 0.0137 15.15 0.44 2713 58 2906 16 12.2 core 100 100 0.99 0.10 0.2094 0.0013 0.5807 0.0145 16.76 0.45 2952 59 2901 10 7.2 patchy 44 43 0.97 0.55 0.2072 0.0024 0.5420 0.0142 15.48 0.46 2792 59 2884 19 9.2 outer 32 14 0.43 0.12 0.1939 0.0028 0.5329 0.0148 14.25 0.47 2754 62 2776 24 1.1 core 45 31 0.69 0.10 0.1927 0.0023 0.4789 0.0125 12.72 0.38 2522 55 2765 20 13.1 rim 75 60 0.81 0.37 0.1896 0.0020 0.5004 0.0128 13.08 0.38 2615 55 2738 17 20.2 outer 100 58 0.58 0.08 0.1890 0.0015 0.5025 0.0125 13.09 0.35 2624 54 2733 13 2.1 centre 73 79 1.08 0.34 0.1867 0.0019 0.4407 0.0112 11.34 0.32 2354 50 2713 16 7.1 patchy 17 11 0.66 1.17 0.1838 0.0061 0.4377 0.0133 11.09 0.53 2340 60 2688 55 18.2 core 58 40 0.69 0.29 0.1830 0.0030 0.3301 0.0086 8.33 0.27 1839 42 2681 27 20.1 core 199 272 1.36 0.09 0.1794 0.0011 0.4206 0.0103 10.40 0.27 2263 47 2647 11 16.1 rim 25 9 0.34 0.58 0.1794 0.0055 0.3751 0.0108 9.28 0.41 2053 50 2647 51 3.1 centre 20 10 0.52 0.39 0.1773 0.0046 0.4003 0.0116 9.79 0.40 2170 53 2628 43 9.1 centre 20 23 1.12 1.44 0.1760 0.0059 0.4002 0.0123 9.71 0.47 2170 56 2616 55 14.1 centre 54 52 0.97 0.51 0.1737 0.0026 0.3804 0.0099 9.11 0.29 2078 46 2593 25 12.1 rim 42 19 0.46 0.03 0.1729 0.0027 0.4847 0.0130 11.56 0.38 2548 56 2586 26 17.2 core 23 11 0.48 0.82 0.1723 0.0063 0.3371 0.0100 8.01 0.40 1873 48 2580 61 5.1 centre 85 63 0.74 0.40 0.1687 0.0032 0.3795 0.0101 8.83 0.30 2074 47 2545 32 4.1 rim 42 29 0.69 0.00 0.1581 0.0017 0.3783 0.0100 8.25 0.25 2068 47 2435 18 19.2 centre 71 58 0.82 0.38 0.1565 0.0026 0.2790 0.0074 6.02 0.20 1586 37 2418 28 19.1 rim 33 21 0.63 6.37 0.1552 0.0080 0.3087 0.0089 6.60 0.41 1734 44 2404 88 10.1 centre 57 37 0.66 0.41 0.1524 0.0027 0.3994 0.0105 8.39 0.28 2166 48 2373 31 17.1 rim 44 29 0.66 0.98 0.1471 0.0037 0.3426 0.0095 6.95 0.28 1899 46 2313 43 18.1 rim 12 4 0.32 1.53 0.1424 0.0087 0.2879 0.0097 5.65 0.42 1631 48 2256106 6.1 rim 33 20 0.60 0.89 0.1393 0.0045 0.2876 0.0080 5.52 0.25 1629 40 2218 56 16.2 core 68 29 0.42 0.55 0.1336 0.0024 0.3245 0.0084 5.98 0.20 1812 41 2145 32 8.1 centre 15 7 0.50 7.10 0.1289 0.0193 0.2685 0.0098 4.77 0.76 1533 50 2083267 15.1 centre 52 54 1.03 0.99 0.1270 0.0043 0.2537 0.0069 4.44 0.20 1458 36 2057 60 6.2 centre 60 46 0.77 1.00 0.1260 0.0039 0.2330 0.0062 4.05 0.18 1350 33 2043 55 11.2 core 114 27 0.24 0.46 0.1251 0.0023 0.2338 0.0060 4.03 0.13 1354 31 2030 32 11.1 rim 30 15 0.51 0.84 0.1250 0.0051 0.2905 0.0084 5.01 0.26 1644 42 2028 72 1.2 rim 44 24 0.54 0.29 0.1221 0.0027 0.2559 0.0068 4.31 0.16 1469 35 1987 40 3.2 tip 48 22 0.46 4.55 0.1175 0.0131 0.2764 0.0083 4.48 0.53 1573 42 1918201

Glenelg inlier s96/41

5.1 core 45 21 0.47 0.63 0.1957 0.0024 0.5401 0.0124 14.57 0.40 2784 52 2790 20 12.1 185 238 1.29 0.19 0.1846 0.0009 0.5186 0.0107 13.20 0.29 2693 45 2695 8 17.1 core 138 81 0.59 0.37 0.1834 0.0012 0.4783 0.0099 12.10 0.27 2520 43 2684 10 15.1 189 209 1.11 0.09 0.1828 0.0008 0.5005 0.0103 12.61 0.27 2616 44 2678 8 10.1 182 60 0.33 0.22 0.1814 0.0009 0.5267 0.0108 13.17 0.29 2728 46 2665 8 11.1 182 22 0.12 0.25 0.1814 0.0009 0.5110 0.0106 12.78 0.28 2661 45 2665 9 1.1 core 32 20 0.61 1.26 0.1802 0.0034 0.4779 0.0116 11.87 0.39 2518 51 2654 31 19.1 147 31 0.21 0.17 0.1780 0.0012 0.4306 0.0090 10.56 0.24 2308 40 2634 11 4.1 348 476 1.37 0.11 0.1767 0.0006 0.4619 0.0093 11.25 0.24 2448 41 2622 6 1.2 rim 1457 463 0.32 0.03 0.1756 0.0003 0.4868 0.0096 11.79 0.24 2557 42 2612 3 16.1 77 86 1.11 0.73 0.1744 0.0019 0.4446 0.0097 10.69 0.27 2371 43 2600 18 1.3 rim 1261 252 0.20 0.05 0.1743 0.0003 0.4653 0.0092 11.18 0.23 2463 41 2599 3 18.1 25 36 1.45 0.92 0.1736 0.0041 0.4648 0.0118 11.12 0.41 2461 52 2592 39 8.1 593 235 0.40 0.09 0.1731 0.0005 0.4577 0.0091 10.93 0.22 2429 40 2588 4 2.1 358 149 0.42 0.15 0.1709 0.0007 0.4619 0.0094 10.88 0.23 2448 41 2566 7 5.2 outer 99 31 0.31 0.51 0.1641 0.0017 0.3781 0.0081 8.56 0.21 2067 38 2499 18 17.2 outer 525 189 0.36 0.05 0.1625 0.0005 0.4470 0.0089 10.01 0.21 2382 40 2482 5 6.2 953 179 0.19 0.06 0.1617 0.0004 0.4313 0.0086 9.62 0.20 2312 39 2474 4 3.1 924 790 0.86 0.08 0.1615 0.0004 0.3914 0.0078 8.71 0.18 2129 36 2471 4 14.1 85 37 0.43 0.77 0.1268 0.0019 0.3600 0.0078 6.30 0.17 1982 37 2055 26 7.1 738 90 0.12 0.13 0.1252 0.0004 0.3575 0.0071 6.17 0.13 1971 34 2032 6 9.1 53 21 0.40 1.29 0.1120 0.0036 0.2360 0.0055 3.64 0.15 1366 28 1832 59 6.1 rim 904 159 0.18 0.10 0.1069 0.0004 0.3089 0.0061 4.55 0.09 1735 30 1747 6 9.2 63 35 0.55 1.57 0.1055 0.0036 0.2388 0.0054 3.48 0.15 1381 28 1724 63 16.2 rim 325 80 0.25 0.15 0.1053 0.0007 0.2873 0.0058 4.17 0.09 1628 29 1720 12 14.2 rim 152 110 0.73 0.47 0.1000 0.0013 0.2641 0.0055 3.64 0.09 1511 28 1624 24 9.3 44 19 0.44 1.68 0.0833 0.0055 0.2016 0.0049 2.32 0.17 1184 26 1277129

Key to spot positions: Unless otherwise stated, analytical spots were centrally located. ‘core’ implies a visible structural core, and ‘rim’ implies a distinct overgrowth. Otherwise, the terms ‘centre’ and ‘outer’ and/or ‘tip’ are used. ‘patchy’ indicates a domain lacking in concentric growth zonation. Detailed spot locations are unfortunately not available for the Borgie sample.